CVE-2024-26658

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> bcachefs: grab s_umount only if snapshotting<br /> <br /> When I was testing mongodb over bcachefs with compression,<br /> there is a lockdep warning when snapshotting mongodb data volume.<br /> <br /> $ cat test.sh<br /> prog=bcachefs<br /> <br /> $prog subvolume create /mnt/data<br /> $prog subvolume create /mnt/data/snapshots<br /> <br /> while true;do<br /> $prog subvolume snapshot /mnt/data /mnt/data/snapshots/$(date +%s)<br /> sleep 1s<br /> done<br /> <br /> $ cat /etc/mongodb.conf<br /> systemLog:<br /> destination: file<br /> logAppend: true<br /> path: /mnt/data/mongod.log<br /> <br /> storage:<br /> dbPath: /mnt/data/<br /> <br /> lockdep reports:<br /> [ 3437.452330] ======================================================<br /> [ 3437.452750] WARNING: possible circular locking dependency detected<br /> [ 3437.453168] 6.7.0-rc7-custom+ #85 Tainted: G E<br /> [ 3437.453562] ------------------------------------------------------<br /> [ 3437.453981] bcachefs/35533 is trying to acquire lock:<br /> [ 3437.454325] ffffa0a02b2b1418 (sb_writers#10){.+.+}-{0:0}, at: filename_create+0x62/0x190<br /> [ 3437.454875]<br /> but task is already holding lock:<br /> [ 3437.455268] ffffa0a02b2b10e0 (&amp;type-&gt;s_umount_key#48){.+.+}-{3:3}, at: bch2_fs_file_ioctl+0x232/0xc90 [bcachefs]<br /> [ 3437.456009]<br /> which lock already depends on the new lock.<br /> <br /> [ 3437.456553]<br /> the existing dependency chain (in reverse order) is:<br /> [ 3437.457054]<br /> -&gt; #3 (&amp;type-&gt;s_umount_key#48){.+.+}-{3:3}:<br /> [ 3437.457507] down_read+0x3e/0x170<br /> [ 3437.457772] bch2_fs_file_ioctl+0x232/0xc90 [bcachefs]<br /> [ 3437.458206] __x64_sys_ioctl+0x93/0xd0<br /> [ 3437.458498] do_syscall_64+0x42/0xf0<br /> [ 3437.458779] entry_SYSCALL_64_after_hwframe+0x6e/0x76<br /> [ 3437.459155]<br /> -&gt; #2 (&amp;c-&gt;snapshot_create_lock){++++}-{3:3}:<br /> [ 3437.459615] down_read+0x3e/0x170<br /> [ 3437.459878] bch2_truncate+0x82/0x110 [bcachefs]<br /> [ 3437.460276] bchfs_truncate+0x254/0x3c0 [bcachefs]<br /> [ 3437.460686] notify_change+0x1f1/0x4a0<br /> [ 3437.461283] do_truncate+0x7f/0xd0<br /> [ 3437.461555] path_openat+0xa57/0xce0<br /> [ 3437.461836] do_filp_open+0xb4/0x160<br /> [ 3437.462116] do_sys_openat2+0x91/0xc0<br /> [ 3437.462402] __x64_sys_openat+0x53/0xa0<br /> [ 3437.462701] do_syscall_64+0x42/0xf0<br /> [ 3437.462982] entry_SYSCALL_64_after_hwframe+0x6e/0x76<br /> [ 3437.463359]<br /> -&gt; #1 (&amp;sb-&gt;s_type-&gt;i_mutex_key#15){+.+.}-{3:3}:<br /> [ 3437.463843] down_write+0x3b/0xc0<br /> [ 3437.464223] bch2_write_iter+0x5b/0xcc0 [bcachefs]<br /> [ 3437.464493] vfs_write+0x21b/0x4c0<br /> [ 3437.464653] ksys_write+0x69/0xf0<br /> [ 3437.464839] do_syscall_64+0x42/0xf0<br /> [ 3437.465009] entry_SYSCALL_64_after_hwframe+0x6e/0x76<br /> [ 3437.465231]<br /> -&gt; #0 (sb_writers#10){.+.+}-{0:0}:<br /> [ 3437.465471] __lock_acquire+0x1455/0x21b0<br /> [ 3437.465656] lock_acquire+0xc6/0x2b0<br /> [ 3437.465822] mnt_want_write+0x46/0x1a0<br /> [ 3437.465996] filename_create+0x62/0x190<br /> [ 3437.466175] user_path_create+0x2d/0x50<br /> [ 3437.466352] bch2_fs_file_ioctl+0x2ec/0xc90 [bcachefs]<br /> [ 3437.466617] __x64_sys_ioctl+0x93/0xd0<br /> [ 3437.466791] do_syscall_64+0x42/0xf0<br /> [ 3437.466957] entry_SYSCALL_64_after_hwframe+0x6e/0x76<br /> [ 3437.467180]<br /> other info that might help us debug this:<br /> <br /> [ 3437.469670] 2 locks held by bcachefs/35533:<br /> other info that might help us debug this:<br /> <br /> [ 3437.467507] Chain exists of:<br /> sb_writers#10 --&gt; &amp;c-&gt;snapshot_create_lock --&gt; &amp;type-&gt;s_umount_key#48<br /> <br /> [ 3437.467979] Possible unsafe locking scenario:<br /> <br /> [ 3437.468223] CPU0 CPU1<br /> [ 3437.468405] ---- ----<br /> [ 3437.468585] rlock(&amp;type-&gt;s_umount_key#48);<br /> [ 3437.468758] lock(&amp;c-&gt;snapshot_create_lock);<br /> [ 3437.469030] lock(&amp;type-&gt;s_umount_key#48);<br /> [ 3437.469291] rlock(sb_writers#10);<br /> [ 3437.469434]<br /> *** DEADLOCK ***<br /> <br /> [ 3437.469<br /> ---truncated---